How do I type a parent-walk?

[cjw296]

Given this code:

T = TypeVar('T')

@dataclass()
class Element(Generic[T]):
    value: T
    parent: 'Element[Any] | None' = None

...

            breadcrumbs = [self.current_element]
            current = self.current_element
            while current := current.parent:
                breadcrumbs.append(current)

self.current_element is always of type Element[Any].

The above code causes mypy to complain:

error: Item "None" of "Element[Any] | None" has no attribute "parent"  [union-attr]

How do I add annotations such that mypy can understand what's going on here?

[hauntsaninja]

That seems like a bug in mypy, I would type ignore.

[cjw296]

Hah! Well, happy to hear that then... do I need to submit a mypy bug or has it already happened?

[cjw296]

Any news on this?

[JukkaL]

Creating a mypy issue could help move this forward.

[cjw296]

python/mypy#18608